Tape recorder



July 30, 1963 L. D. BARRY 3;099,709

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July 30, 1963 L. D. BARRY TAPE RECORDER Original Filed May 27, 1952 4 Sheets-Sheet 3 WM ac 2 55 m Wigs La 257mm ZM6R00/V0 fly. /0

ZVMOUN AC. B/Af/NG 0.7011470 VIDEO AMP! lF/ER INVENTOR.

July 30, 1963 Original Filed M fly. f2 14 L. D. BARRY 3,099,709

TAPE RECORDER ay 27. 1952 4 Sheets-Sheet 4 SHOW/V IN F76. IZ

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United States Patent ()filice 3,099,709 Patented July 30, 1963 This invention relates to tape recorders and in particular to a method and means for recording and reproducing signals for television pictures, sound, and other information. This application is a continuation of my co-pending application, Serial No. 292,013, filed May 27, 1952, now abandoned.

Magnetic tape recorders have long been made for recording sound and information with accompanying efforts to improve the magnetic medium and thereby lower the tape speed or increase the audio frequency response at a given speed. By providing a recorder which transversely scans the tape together with special circuits for recording and reproducing over a wide frequency range this improved tape recorder is not only suitable to apply the required audio frequencies to the tape at a much lower tape speed, but it is also designed for recording video signals which have a frequency range of about to 4 me. with a linear velocity of tape comparable to present sound tapes.

One object of this invention is to provide a tape recorder for video signals by which these signals can be picked up in a television receiver, recorded, and reproduced from the record as often as desired to be played back on a television picture tube.

A second object is to provide a system of scanning a tape to enable more information to be recorded on a given length of tape.

A third object is to provide a combination sound and video magnetic tape recorder.

A fourth object is to provide a recording system for video which minimizes critical adjustment, is simple to operate, is conveniently sized, and has tolerances and design suitable for manufacture.

A fifth object is to provide a television recorder which does not interfere with the viewing of the television program on the picture tube of the television set from which the video signal is being recorded.

Other objects have been taken into consideration within the limits of invention resulting in further im provements in the art of tape recording disclosed herein.

The development of this invention required consideration of several problems.

In accordance with present standards the frequency required to be passed in a video amplifier is 04,000,000 cycles/sec. for a high quality picture. A good picture can be produced with 303,600,000 cycles, and the more limited the frequency range the poorer the resolution of the picture.

The present magnetic recording media have a good level output from 20' to about 5000 cycles at 3.75"/sec. The output volume is equalized by circuits to give a practically flat response in this range. Using a figure of 5000 cycles at 3.75"/sec. present day tape will record 1333 cycles/inch. The frequency response is directly proportional to the speed. To record video on tape or wire to include 4 mc. would take 4 mc./ 1333:3000" of medium/sec.

As a feature of this invention a rotary wheel or disk is provided having recording heads thereon appropriately spaced to scan the tape crosswise for recording and pickup at a peripheral speed of approximately 3000/sec. The tape is curved to conform to the contour of the wheel.

Keeping the size suitable for portability the following example is given to show the relations of dimensions and speeds. Calculations are based on accepted television standards providing for interlaced scanning 30 frames/ sec., 525 lines/frame, and 0-4 rnc. video frequency response.

The frequency response required of each horizontal video line is:

4,000,000 cy./see. 525 lines/frameX 30 frames/sec.

Recording at high speed the tape should still take 1333 cy./inch.

Then the tape Width required for each horizontal line and retrace is:

254 cy./line 1333 cy./inch A wider tape per horizontal video line requires a higher peripheral velocity for scanning but would give a better frequency response and a higher output it needed. A narrower video track would give a lower frequency response and output level, but the peripheral velocity would be less. Allowance for overlap and other factors mentioned later requires a wider tape than the line of signal to be reproduced.

Selecting 8 as the diameter for the wheel the spacing of the magnetic heads around the periphery=0.191".

The retrace takes (016 to 0.18) picture width of video track.

Then picture width=P.W. -0.1910.17 P.W.

The tolerance is $0.01 0.163=i0.0016 This is Within standard practice and is the tolerance of variation for spacing the heads around the Wheel.

The number of heads=8 3.1416/0.191=132 heads.

Increasing the width of the tape to include eight horizontal video lines, the number of heads is reduced to sixteen with a slight increase in diameter.

The r.p.m. of the Wheel=525 30 60/(8 X 16) :7390 r.p.m.

To reduce the r.p.m. to 5000 then requires a different number of heads and a larger diameter for equal clarity under given conditions.

Number of heads=525 X30X60/(8 X 5000) :236524 heads Diameter=24 0.191 8/3.1416 =11.67".

Using ring-type heads with a 0.0005 gap a width of 0.01 should be suflicient for the pole tips and approximately equal to the width of line recorded. With a 0.01" spacing between lines to prevent demagnitization where the picture has changed the linear space/line totals 0.02".

The linear speed of tape=525 30X 002/ 8-=39.4"/ sec.

This is faster than required for sound recording, and can be reduced if a narrower pole piece or little or no spacing between lines is found to produce a satisfactory picture. The spacing between lines is not considered a necessity and would not be used if only one horizontal video line was recorded per recorded line across the tape width since, the lines if aligned properly would build up a field of picture as the cathode ray does on the tube. The succeeding fields would not be interlaced on the recording but would be interlaced by the picture tube.

It should be understood that any improvement in the frequency response of the tape or magnetic heads over present standards would improve the picture reproduced, or reduce the r.p.m. or diameter of the wheel for a given quality of picture, and improve the sizing and speed of the tape and associated par-ts.

=0.191/line In the drawings:

FIGURE 1 is a top plan View of the improved tape recording mechanism, the enclosure and electrical circuits being removed;

FIGURE 2 is a front elevation of the recorder shown in FIGURE 1;

FIGURE 3 is an enlarged side elevation of the operating lever assembly in FIGURES 1 and .2;

FIGURE 4 is an enlarged section view of the tape guide assembly taken on line 44 in FIGURE 1;

FIGURE 5 is an enlarged edge view of the wheel in FIGURES 1 and 2 part being broken away to show the coil connections to commutator segments and general construction;

FIGURE 6 is a side view of a portion of the wheel shown in FIGURE 5 further enlarged and broken away to show details of the magnetic heads and segments;

FIGURE 7 is a plan view of a piece of tape to show the sound and video magnetic track; portions thereof being labeled. The tWo fields of the picture are outlined and labeled thereon to show the sequence in which they are recorded;

FIGURE 8 is a block diagram of a television receiver with a recorder connected thereto;

FIGURES 9 and 10 are combination block diagrams and electrical schematics of two variations of the recording circuits;

FIGURE 11 is a schematic and block diagram of the reproducing circuits;

FIGURES 12 through 17 are curves representing the signal at successive points in the process of recording and reproducing;

FIGURES 18 and 19 are schematic views of two alternative arrangements for scanning the tape.

Referring to the drawings and in particular to FIG- URES 1 and 2, 20 is a supply reel and 22 is a take-up reel for magnetic tape 24, which as seen from FIG- URE 1 is inserted between wheel 26 and groove 28 of guide 29. Guide 29 as seen in cross section in FIG- URE 4 has retaining sides 30and 31 and edge covers 32.

and 33 which hold the tape on both sides of wheel 26 so that the tape will not leave the groove 28 by friction of wheel 26 when rotating against the tape. Guide 29 holds the tape against the periphery of wheel 26, groove 28 being curved to the radius of the wheel, and guide 29 exerts a light force against the wheel by spring 36 and pivot bar member 38 which being pivoted at two points 40 and 41 in line hold the guide 29 against wheel 26 substantially parallel. to the axis of the wheel. Guide 29 has an inserted cushioning pad or gap 44 at the line of contact of the wheel and guide so that when the tape is inserted by pushing guide 29 away from the wheel the tape will have a slight give in contact with the wheel which will save the tape from excessive wear and provide close even contact.

An erasing head 46 bears on the tape 24 along groove 28 head of the Wheel. Spring 48 furnishes the required pressure, and pad 50 insures good contact. Head 46 covers the full width of magnetic media.

A sound recording head 52 bearson tape 24 after it passes the wheel. The head magnets are just wide enough to cover the sound track on the tape. Spring 54 provides the desired contact pressure.

The erase and record heads are each supported by pivoted arms 56 and 58 respectively. The heads are curved to fit groove 28 and help hold the tape in the groove and steady it. The design principles of the heads are similar to any used for sound erase or recording. A.C. erase is not objectionable because slight variations in the tapes longitudinal magnetism will not effect transverse scanning. The sound could be put on over the Whole video track if desiredas long as the tilt of the sound recording head is adjusted to the slant of the transverse scanning and the proper biasing and limiting ofthe amplitude of the signals is used.

Wheel 26 is driven by constant speed motor 60 through coupling 62, shaft 63, spur gear 64 engaging spur gear 66, shaft 68 to which wheel 26 is fixed. Gears 64 and 66 increase the speed to shaft 68. Gear 64 is preferably a fiber gear as should one of every gear set to reduce noise and vibration. Guard 69 encloses most of wheel 26. Spring washer 70 prevents axial movement of wheel 26.

Tape 24 is driven by motor 60 through beveled gears 71 and 72, shaft 74, worm 76, worm gear 78 fixed on shaft 86 coupled to shaft 82 by a friction clutch 84, and sprocket tooth drive wheel 86 having teeth which engage holes 88 in tape 24. The tape is moved by this tape transport from left to right during record and playback at a speed having a fixed relationship to the rpm. of the wheel 26. Thereby recordings can be reproduced even with slight variation in motor speed.

The take-up reel is driven by its motor 90 during record and playback. The supply reel is driven at a relatively high speed for rewind by its motor 92. This practice is followed in some quality tape recorders.

Lever 94 provides means for the operator to shift from a neutral position N to either a position for record and playback F in which lever 94 is shown or a position for rewind R. FIGURE 3 shows the details of lever 94. This lever is pivoted about bearings 96 and 98 on shaft 160. The lever has four parallel arms extending to bearings 102 and 103 holding shaft 80 and bearings 105 and 106 holding shaft 82. Shaft 82 has the sprocket drive 86 fixed thereon. The friction clutch 84 held together by spring 198 permits slippage whenever worm gear 78 is engaged with worm 76 upon the operator moving lever 94 to position F or whenever the force to pull the tape exceeds a safe limit. The amount of slippage decreases until the tape gets up to speed.

When lever 94 is brought to positions N and R lever 110 moves guide 29 away from wheel 26 disengaging the tape from the wheel. Lever 110 is actuated by link 112 to lever 94 and bears on 38 in positions N and R.

Lever 94 also actuates switches, not shown, to control power to the reeling motors 90 and 92. The usual switching and safety features, should be provided.

Wheel26, as seen in FIGURESv 5 and 6, is composed of two nonmagnetic disks 116 and 117 bolted together with bolts 118. Disk 117 is brazed or otherwise secured to shaft 68. Recording-reproducing heads 12% are symmetrically spaced about the circumference of wheel 26 in a space 122 provided by grooving the adjoining faces of each disk. Each head has two coils I24 and 125. The two coils are connected series aiding and the ends brought to individual commutator segments arranged in two concentric rings 126 and 127 around the side of the disk 116. The coils are similar and similarly connected to the segments so that any signal recorded or picked up will have the same polarity and value independent of which head recorded or picked it up. The cores 128 are in twoparts to facilitate winding and are securely fastened to disk 1116 by screws 129 through overlapping parts of the. cores 128. Copper brushes 1132 and 133 engage concentric rings 1 26 and 127 respectively to carry the signalsbetween the coils and the recording-reproducing circuits- The commutator segments and brushes I prefer to call electrical switching means.

When in reproducing a head comes in or out of con tact with the magnetic medium at the ends of the line being scanned the coils receive a voltage surge from any magnetization from the signal, bias, or erase that is present. This is not part of the signal to be picked up; it is a discontinuity which has caused this surge. Therefore the signal is recorded with enough overlap in scanning successive lines to provide for the period of this voltage surge to end before the coils are contacted by the brushes connecting them to the reproducing circuits. This is easily done by changing to a narrower set of brushes than were used for recording or by using separate coils and a commutator ring for pickup with brushes having the desired coverage. A slip ring could provide a common for one side of all coils. The recording should be made with sufficient overlap so that there will still be a slight amount of overlap with the narrower brushes to prevent an open circuit interruption of the signal.

FIGURE 7 shows the tape 24 as it would pass under the heads shown in FIGURE 6. The tape has a sound and a video track so labeled. Fields 1 and 2 follow in sequence and are composed of a suitable number of horizontal lines of video per line of width labeled Reproduced Signal. To pick up this Reproduced Signal the video track includes Alignment and Contact Allowance that is an overlap provided for the distance required by the brushes to come from no contact to sufficient contact with the segments and allowance for tolerance in spacing heads, commuator segments, positioning of guide 29, and other variables. This overlap added at the entrance and exit of the Reproduced Signal equals the Picked Up Signal. Adding Voltage Surge Allowance gives the required minimum Recorded Video Signal per transverse line. The magnetic medium can be wider than this minimum width.

Referring to FIGURES 8, 9, and 10, the recorder picks up a signal at the output of the video detector where it has been rectified and filtered of the LF. carrier. The recorder is preferably provided with its own video amplifier with circuits designed to give any desired preemphasis as in sound recorders to balance the response over the frequency range. The signal is put in the video amplifier. The output thereof is connected to a DC. restorer, FIGURE 9, as required if the circuits of the video amplifier do not pass the 13.0. component and so that the signal might also be picked up after any TV video amplifier as indicated by dash lines, FIGURE 8. -In FIGURE 10 the DC. restorer was omitted. The signal is next fed to a novel amplifier one form of which is shown in FIGURE 9 and another form in FIGURE 10.

Referring to FIGURE 9, the signal is then applied to the grid of tube 140. A voltage supply 131+ is connected to the plate of tube 140 through resistors R1 and R2. R1 being connected between B=1+ and a junction point J71. The circuit of the head coils 124 and 125 is connected by segments 126 and 127 respectively engaging brushes i132 and 133 across points J1 and 32+ in series with an equalizing network represented by a condenser C1 and resistor R3 in parallel. B2+ has a potential equal to or less than 31+. Grid bias is provided for tube 140 across R4.

The input signal would probably vary from to 75 volts. The zero voltage signal on the grid would represent a white picture in the TV cathode ray tube and -50 to -75 volts black. Tube 140 is fully conducting with zero grid volts and decreases in conductivity linearly from 0 to 75 volts. J1 is at a minimum potential for this point when tube 140 is fully conducting and maximum when tube 140 is nonconducting. The difference in potential between Jtl at max. .and min. can be adjusted by varying R1, R2, and B2+ so that the current through coil-s 1 24 and 1 25 can vary as desired. Adjustment can be made to give varying -D.C., A.C. with a DC. component, or pure A.C. Varying D.C. can thus be provided having the proper DC. bias for recording. 01' using an AC. bias oscillator of high frequency the adjustment is made to provide A.C. alone.

The A.C. bias frequency should be several times the maximum recorded frequency. Since the tape takes at least a biasing frequency of 30,000 cy. recording 5000 cy.; the tape should take 6 4 mc.=24 me. bias for recording 4 mo. Therefore an AC. biasing oscillator is shown in block diagram with an adjustable resistor R to select the best biasing current. The oscillator output circuit is tuned by a small capacitance C2 and inductance L to prevent shorting of the signal through the oscillator.

Referring to FIGURE 10, this circuit for driving the coils differs from the circuit of FIGURE 9 in that two tubes are used in place of and a complete bridge circuit is formed. The bridge is formed by tube in series with resistor R10 and tube 152 in series with resistor R11 in opposite legs of the bridge, the plate side ends of the legs of both tubes 150 and 152 connected together by a third leg containing resistor R12, and the cathode side ends of the legs connected together as the fourth leg containing resistor R13. The plate side of the leg of tube 152 is connected to voltage B3 and the cathode side of the leg of tube 150 is grounded to B3. Coil 124' with equalizing circuit represented by C3 and R14 is connected as a bridge from the plate side of the leg containing tube 150' to the cathode end of the leg containing tube 152. The tubes are peutodes or triodes and have their grids connected to the input signal and biased to a negative potential B4- connected to the grids by a high resistance R15.

When the tubes are full conducting with zero grid voltage, for example, current flow is from B3+ to B3 through tube 152, R11, coil 124', R10, and tube 150 in series. The tubes decrease in conductivity linearly as the grid voltage swings from 0 to 75 volts and as they do the potential across the bridge changes linearly. The polarity and potential across coil 124 is determined for a given signal input according to the biasing of the grids, tube characteristics, and values selected for the resistors. The plate voltage is high enough to provide linear operation. Thus varying D.-C., A.C. with a DC. component, or pure A.C. can be provided. The proper values being selected according to whether AC. or D-C. biasing is used as with the circuit in FIGURE *9.

Steps in the process of recording and reproducing a signal are shown by reference to FIGURES 12 through 17.

FIGURE 12 shows a typical signal from the TV deteotor, not to scale.

FIGURE 13 shows the output from an odd number of amplifier stages thus reversing the signal, the DC. voltage component being restored by the DO. restorer if it Was missing at input or lost in the video amplifier.

FIGURE 14 shows the signal as recorded with DC. biasing, the polarity of the bias voltage being such as to reduce the magnetization left by the saturating erase magnet. If a minus voltage was used for biasing the tape the zero reference line would be at the top by an equal distance above the bias voltage line. The max. and min. lines represent the recording current at limits of linearity :of recording on the magnetic medium.

FIGURE 15 shows the signal with DC. components removed ready for recording with A.C. biasing.

FIGURE 16 represents the net signal recorded with either AC. or DC. biasing. The flux lines are omitted for simplicity. The flux density is indicated by the distance the curve departs from the zero reference line. The flux lines if shown would loop from the vertical faces only. Lines through the zero reference represent complete reversal of the direction of magnetization as indicated by the letters N and S.

FIGURE 17 shows the signal voltage picked up by the coils. Each increase of magnetization in one direction in- (1111068 a voltage of one polarity, and each decrease or reversal of magnetization therefrom induces a voltage of the opposite polarity in the coils. The intensity of this induced voltage in either case is proportional to the rate of change of flux linking with the coils.

The circuit shown in FIGURE 11 is a practical means developed to reproduce the original signal. This circuit receiving these intermittent voltages adds and subtracts charges in accordance with the voltage induced with reference to a linear rate of changing and discharging condenser C4. The amplifying portion of this circuit is assumed [t0 be designed to supply post-emphasis.

Referring to this circuit, two similar tubes and 161 are provided. One end of the pick-up coil 124" is connected to the grid of tube 160 and the other end connected to the grid of tube 161. Equally matched resistors R21 and R22 connected in series across the grids of tubes 160 and 161 provide a balanced grid bias voltage fir-om a source of negative potential B. The cathodes of tubes 160 and 161 are grounded, and the plates. are connected in series with equal resistances R23 and R24 respectively to B6+ voltage supply. The plates of tubes 160 and 161 are also connected to the grids of tubes 164. and 165 respectively in series with condensers C5 and C6 respectively. Grid leak bias is provided for tubes 164. and 165 by resistors R25 and R216 respectively. The cathode of tube 165 is grounded through R27 and the plate connected to (the cathode of tube 164. The plate of tube 164 is connected in series with resistor R28 to a positive potential B7+. The plate of tube 165 isconnected to condenser C4- in series. with a current limiting resistor R29 to form an integrating circuit. The other side of C4 is grounded. The output across C4- is fed to -the grid of a. video amplifier providing if desired further postaemphasis from which the signal is returned to the TV ahead. of its video amplifieras seen in FIGURE 8. The circuit connecting the recorders output to rthe TV has ahigh resistance R30 in series .to prevent excessive current caused by improper connection oroperation. The connecting leads shouldbe fused where the recorder is to be a separate unit connected and disconnected from the TV set.

A voltage induced in coil 124" will place opposite changes on the grids of, tubes 160. and 161. The bias voltage-supplied by BS- will be such that the tubes 160. and 161 will operate as class A amplifiers. When no signal-is'bcing receivedcondensersCS and 06 have equal charges and the biasing can be suchthat tubes 160 and 16-1 conduct. A signal will cause one tube to conduct more and theother less. according to the polarity of the signal. The tube which conducts less increases the. change .on its plate condensers and this increases the positive value of the grid of-v the associatedtube164 or 165. causing this. tubeto conduct if biasedto cutoff, withno signal or. to conduct to a greater extentif notbiasedto thatextent.

Withasufiiciently high voltage applied at 137+, tube 164, conducts, chargingthe upper plate of capacitor C4 positive and the. plate of tube .165, positive until tube165 becornesconductive. A positive signal (reduction of, negative charge) onthe grid of tube 165 will causeconduction, reducing the positive change on the upper plate of C4andthe cathodeoftube 164-.enabling tube 164'to be more, readilyconductive when its grid receives. a. positive charge, thus capacitor C4. gains and-loses changes aboveand below its initial charge. The signal is..algebraically integrated on condenser C4 in that both positive and negative charges areadded thereon, the negative be.- ing subtractedfromthe positive.

'I ubes 164 and 165 will be biased to the same point of conductivity with no signal and are preferably biased to cutoff with no signal. Thus when .a .signal increases the grid potential of tube 164. that tube conducts and increases the potential on C4. When a signalof reverse polarity isreceived this increases the gridpotential of tube 165, and that tube conducts and decreases the po+ Itential on C4. Thus the charge on C4- can be added and subtracted. The circuit is balanced to add and subtract changes on condenser 04 on a linear basis, whereby the output voltage across C4 is pnopontional to .fEat' of the appliedsignal voltage which will be pure A.C as seen from FIGURE 17 and therefore balance out the signal charge on C4. The effect of a signal. charge-on C4 in. influencing conductivity can be made negligible. The cathode of tube 165 can be connected to a negative ;potentialbelow ground if this is found desirable to enable it to have a suflicient potential difierencebetweenplate and cathode to conduct.

The circuits for the sound are similar to present-day sound tape recorders and are therefore not shown.

When reproducing -a recorded signal on a TV receiver the lines of recording are synchronized with the scanning of the tape by retarding the tape manually by applying a slight force to slipping clutch- 84, FIGURES l, 2, and 3, until the wheel 26 scans on the lines and not between lines if the recording was made with space between lines; otherwise this adjustment is not necessary. The magnetic head scanning wheel 26 should be free from Wobble and vibration, and is held against axial movement as described so that the path of the magnetic heads therein will not vary beyond allowable tolerances.

Two variations in the arrangement for scanning are shown in FIGURES 18 and -19. Other methods of scan ning tape with transverse movement include a reciprocating head or heads, and heads mounted on and moved by end-less belt.

FIGURE 18 shows two tapes 24' and 24" being scanned by wheel 26 the heads thereof being located on the side in aring contacting the tapes and concentric with the axis ofthe wheel. The resulting transverse scan will be curved to the radius of the circue of the heads and will enable a slightly longer transverse line for a given width of tape than with the scanning wheel rotating perpendicular to the face and edge of the tape. The tape is fiat when scanned. Rollers and 181 hold the tapes 24-' and '24 respectively against the heads on wheel 26'.

TWoo-r more tapes can be simultaneously scanned by one wheel and two or more recording and reproduction circuits provided. Some applications are the making of several recordings, the blending of pictures, or the quick change from-one tape recording to another.

FIGURE l9 showsdisk 26' scanning tape 24" at an angle. This inclined scanning is intermediate between the type of scanning shown in-FIGURES 1 and 2 and that shown in FIGURE'18; The curvature of the tape is reduced as the angle of the wheel fromperpendicular is increased.

Variations in the type of magnetic heads, the circuits for recording and reproducing, the contacts between the wheel and the stationary circuits and other variations may readilycome to mind: herewith. This recorder can be adaptedtorecord'sound -or information atvery slow tape andscanning wheel speed simply by providing a slow speed drive; for example, motor 60 could be replaced with age'armotor. Thisrecorder can be developed for use in conjunction witha TV'camera for recording pictures for later broadcast or for direct replay on individual TV receivers.

Magnetic tape is-.-also called magnetic film especially when used in 16 and 35 mm. sizes. The word magnetic tape is herein meant to include magnetic film.

Althoughlhave shown and-described only one form of recorder, together with a few variations oft-he method of: scanning, embodying my invention, it is understood that various changes, modifications, and adaptations may be made therein within the scope of the appended claims without departing from the spirit and. scope of my inventlon.

What is claimed is:

1. A magnetic tape recorder for recording and reproducing electrical signals which comprises, in combination, -a frame, a scanningvwheel rotatably supported on said frame, a plurality of magnetic heads equally spaced around said wheel .in an axially concentric circle, means connected to said wheel for rotating the same at constant speed, a magnetic recording tape having a-width larger than; the spacing between said heads, a tape transport on said frame for longitudinally movingsaid magnetic tape across said wheel in contact withv said heads over an arc interval wider. than the spacing between said heads at a speed proportional to the angular velocity of said wheel, recording. circuitmeans, means for electrically connecting said heads to said recording circuit means while the heads are in position for contact with said tape during recording, reproducing circuit means, means for individually connecting said heads to said reproducing circuit means only when said heads are scanning said tape for are intervals included in arc intervals covered by said heads while recording to thereby scan transversely in shorter lines for reproducing than for recording and eliminating from the reproduced signal voltage surges in the heads resulting from engagement and disengagement of the heads with the recorded magnetic tape, and means for selectively connecting said first mentioned connecting means and said second mentioned connecting means to said heads.

2. A magnetic tape recorder for reproducing a signal represented by successive lines of recording extending transversely of :a magnetic tape, which comprises a rotatably mounted scanning wheel, magnetic heads spaced around the periphery of said wheel, means connected to said wheel for rotating the same, means for longitudinally moving the magnetic tape in magnetic proximity to said heads at a speed proportional to the angular velocity of said wheel, circuit means for reproducing signals, electrical switching means for connecting said heads to said reproducing circuit means while scanning transversely only the central portion of each transverse line of recording, thereby eliminating voltage surges from the reproduced signal caused by the engagement and disengagement of the heads in magnetic proximity to said lines of recording, and means for connecting said heads to said switching means.

3. A magnetic recorder in accordance with claim 2, wherein each of said heads includes a coil having two terminals, said switching means includes a commutator secured concentrically to said wheel to rotate therewith, said commutator including a plurality of segments, one terminal of each head being connected to one segment of said commutator, brush means for connecting each commutator segment to said reproducing circuit means for a smaller angle of subtended arc for signal reproducing than for recording, and means for electrically connecting the other terminals of said heads to said reproducing circuit means.

4. A magnetic tape reader for reproducing a signal represented by successive lines of recording extending transversely of a magnetic tape which comprises, in combination, a rotatably mounted scanning wheel having a plurality of circumferentially disposed magnetic heads aligned in a plane, means for guiding said tape in magnetic proximity to and across the path of said magnetic heads, means connected to said wheel for rotating said scanning wheel at substantially constant speed, means for moving said tape at :a linear speed proportional to the angular velocity of said wheel, circuit means for reproducing the signal recorded on said tape, switching means for connecting successive heads to said circuit means only while scanning the central portion of each line of transverse recording, means for connecting said heads to said switching means, said reproducing circuit means including an integrating circuit means in which voltage impulses of the same polarity are added and those of opposite polarity are subtracted to provide an algebraically integrated output signal resembling the recorded signal.

5. A magnetic tape recorder and reproducer compris ing a rotatably mounted scanning wheel, a plurality of magnetic heads spaced on said wheel along an axially concentric circle, a segmented commutator means connected concentrically to said wheel to revolve with said wheel, successive heads being connected to successive segments of said commutator means, recording brush means for connecting said commutator means for recording, playback brush means for replacing said recording brushmeans for connecting the segments of said commutator means successively over less degrees of :arc than said recording brush means, whereby each head is eifective 10 for reproducing the recorded signal only while that head is within the recorded portion of the tape.

6. A magnetic tape recorder and reproducer comprising a rotatably mounted scanning wheel having a plurality of magnetic beads spaced and secured thereon, means for continually moving the magnetic tape across said wheel so that said wheel scans the tape substantially transversely, recording and reproducing circuit means, and commutator and brush means connected to said heads for successively and overlappingly rendering said heads effective for re cording :and reproducing, the heads being rendered effective during reproducing over a shorter arc of said movement than, and within, the arc of head movement in which the tape is recorded, and means for selectively connecting said commutator and brush means to said recording and reproducing circuit means.

7. In a magnetic-tape recorded-signal reproducer for pictures having a rotatably mounted scanning wheel with a plurality of magnetic heads spaced therearound, means connected to said wheel for rotating the same, and means for continually moving said tape across said wheel in contact with said heads to reproduce successive lines of transverse recording on the tape, the combination comprising reproducing circuit means, and switching means successively connecting said heads to said circuit means only for an interval of arc movement of each head, the arc interval extending from a point where the head is in full contact with a recorded line on a tape to a point before the head leaves full contact with the recorded line.

8. A recorder in accordance with claim 7, wherein said scanning wheel comprises a pair of parallel coextensive disks, means securing said disks together, the circumferential edges of the outward face of each disk being rounded, each magnetic head including ring-shaped core pieces and two windings on said core pieces, the core piece-s being secured to one of said disks on the face thereof facing the other of said disks with the pole tips thereof substantially flush with the circumferential edge of the said disks, said switching means including a commutator which is secured concentrically to said one disk, the windings of said heads being connected to said commutator.

9. In a reproducer of pictures recorded on a magnetic tape in a plurality of successive transverse lines each of which has more than the information required to be reproduced, each line being recorded with a current varying with wicture brightness, said reprodu-cer comprising a rotatably mounted scanning wheel having -a plurality of magnetic heads, means connected to said wheel -for rotating the same, and means for continually moving said tape across said wheel in magnetic contact with the heads to scan the tape along the recorded lines, the combination comprising reproducing circuit means, switch means connecting said heads to said reproducing circuit means over an are included within the recorded are, thereby reproducing a central portion of the length of each recorded line on the tape, said reproducing circuit means including integrating means for restoring the differentiated picture signal at the output of the heads to the picture sign-a1 as recorded.

10. A combination video and sound recorder comprising, in combination, a tape transport for moving magnetic tape, an audio magnetic head engaging said tape along one edge thereof for recording sound along a track parallel to the length of said tape, a rotatably mounted transverse-scanning magnetic-recording wheel having :a plurality of heads thereon, drive means connected to said wheel for rotating the same so as to transversely record picture lines of video signals across said tape, a tape guide movable between a first position in which the tape is in engagement with said wheel to second position in which the tape is disengaged from said wheel, switch means for activating said tape transport, said switch means moving said guide to said first position when said tape transport is activated and to said second position when said wheel is rotating and said transport is stopped, said tape guide being free to :be moved from said first position while said transport is activated, said audio head being mounted to remain in engagement with said tape when said tape is disengaged from said wheel.

11. A method of magnetic recording and reproducing of video signals which comprises the steps of recording video signals on a magnetic tape in successive parallel transversely extending lines, the end of each line and the beginning of the next line being simultaneously recorded with the same signal and at substantially the same recording strength as used along the central portion of that line, and reproducing only the central portion of the length of the recorded lines including part of the recorded overlap.

12. A tape recorder in accordance with claim 1, wherein said tape transport is arranged to carry the magnetic tape on edge, the wheel is rotated in a plane extending perpendicular to the tape, the heads are on the outer periphery of said wheel, a guide block is provided which has a concave radial groove in a side thereof to atorm said tape to the circumferential contour of said wheel, means is provided for securing said block to said frame in such a position as to guide said tape past the downward moving side of the circumference of said wheel, and a projection on said block supports the lower edge of said tape against rotation of said wheel.

13. A recorder in accordance with claim 1 wherein said reproducing circuit means is capable of reproducing substantially direct current signals.

14. In a recorder utilizing a magnetic recording tape, information being recorded on the magnetic tape in successive transversely extending @lines with overlap of information on the beginning of one line and the end of the preceding line, a scanning wheel with magnetic beads spaced therearound for successively scanning the magnetic tape to read the lines recorded :on the medium, the spacing between the heads being slightly less than the width of the tape so that the same signal is read by successive heads during the overlap, a reproducing circuit means, and

' switching means connecting said heads to said circuit means only after said heads are fully engaged with the recorded line on the tape and for an interval only within the recorded line on said tape.

15. A recorder in accordance with claim 14 wherein said wheel comprises a pair of parallel coextensive disks, means securing said disks together, the edges of the outer faces of said disks being rounded, a groove on the inner face of each disk which is concentric with the axis of the disk, the groove being of a size to receive the winding of said heads, and the radius of the groove is such that the poles of said heads are substantially flush with the circumdference of said disks.

16. A recorder in accordance with claim 14 wherein said switch means includes a commutator having a segment for each of said heads, each head has a winding with two terminals, one terminal of successive beads being connected to successive segments of said commutator, and brush means engaged with said commutator for connecting said heads successively for an arc during reproducing completely within the transversely recorded line on the tape.

17. A recorder in accordance with claim 1, wherein a recording head is positioned relative to said tape to superimpose a recording on and at right angles to the transverse recording on the tape.

18. A magnetic recorder for reproducing video signals comprising, in combination, a magnetic recording tape having successive transverse lines of video recordin g thereon with overlapping of the signal on successive ilines, a wheel having magnetic heads spaced thereabout to scan successive lines recorded transversely across said tape, means for moving the tape across the wheel and in contact with the heads, means for revolving the wheel insynchronism with the movement of the tape, video reproducing circuit means including integrating means, and switching means connecting each successive head to said 12 integrating means only while the head is fully engaged with the recorded portion of the tape.

19. A magnetic recorder for video signals comprising a magnetic tape, a rotatably mounted scanning wheel, means for rotating said wheel, a tape transport for guiding said tape past said wheel, said wheel having magnetic recording heads spaced equally thereabout to engage said tape successively as the wheel turns, the circumferential spacing between said heads being less than the width of the tape, means for driving said tape in synchronism with said wheel so that said tape is scanned in successive lines, said transport including means. for positioning the tape against the wheel around a portion of the circumference of said wheel longer than the spacing between said heads so that before one head leaves the tape the successive head has been on the tape for an interval of overlap of length sufficient to enable successive heads to be connected and disconnected during replay, reproducing circuit means, and means for electrically successively connecting said heads to said reproducing circuit means at substantially constant impedance for a line interval of recording on said tape of a length longer than the arc length between said heads, thereby recording each successive line with sufficient overlap to enable a central portion of successive lines to be replayed with overlap at full signal strength by successive heads on a reproducing device.

20. A magnetic tape recorder for recording and reproducing electrical signals comprising a frame, a scanning Wheel rotatably mounted on said frame, a plurality of magnetic heads carried by said wheel, said heads being equally spaced around a circle which is in concentric relationship with said wheel, means on said frame for rotating said wheel at a constant speed, means connecting said rotating means to said wheel, a magnetic recording tape having a width larger than the spacing between said heads, a tape transport on said frame for continually moving said magnetic tape longitudinally across said wheel so that each head is in contact with said tape over an arc interval wider than the spacing between heads and at a speed proportional to the angular velocity of said Wheel, recording circuit means, reproducing circuit means, means for selectively coupling said heads to said recording circuit means and to said reproducing circuit means, and means for rendering said heads elfective for scanning a greater are interval when connected to the recording circuit means than when connected to the reproducing circuit means.

21. A magnetic tape recorder for recording and reproducing electrical signals comprising a frame, a scanning wheel rotatably mounted on said frame, a plurality of magnetic beads carried by said wheel, said heads being equally spaced around the periphery of said wheel, means on said frame for rotating said wheel at a constant speed, means connecting said rotating means to said wheel, a magnetic recording tape having a width larger than the spacing between said heads, a tape transport on said frame for longitudinal-1y moving said magnetic tape generally perpendicularly to the plane of rotation of said wheel, a guide block having a concave radial groove in a side thereof for forming said tape to the circumferential contour of said wheel, means securing said block to said frame in such a position as to hold the tape against the periphery of the wheel, a gap disposed in said guide block at the line of contact of the wheel and the guide block, said tape being moved at a speed proportional to the angular velocity of said Wheel, recording circuit means, reproducing circuit means, means for selectively coupling said heads to said recording circuit means and to said reproducing circuit means, and means for rendering said heads effective for scanning a greater arc interval when connected to the recording circuit means than when connected to the reproducing circuit means.

22. A magnetic tape recorder for recording and reproducing electrical signals comprising a frame, a scanning 13 wheel rotatably mounted on said frame, a plurality of magnetic heads carried by said wheel, said heads being spaced around the periphery of said wheel, means on said frame for rotating said Wheel at a constant speed, means connecting said rotating means to said wheel, a magnetic recording tape having a width larger than the spacing between said heads, a tape transport on said frame for longitudinally moving the magnetic tape across said wheel, a tape guide movable between a first position in which the tape is in engagement with said wheel to a second :position in which the tape is disengaged from said wheel, switch means for activating said tape transport, said switch means moving said guide to said first position when said tape transport is activated and to said second position when said wheel is rotating and said transport is stopped, recording circuit means, reproducing circuit means, means for selectively coupling said heads to said recording circuit means and to said reproducing circuit means, and means for rendering said heads efiective for scanning a greater arc interval when connected to the recording circuit means than when connected to the reproducing circuit means.

References Cited in the file of this patent UNITED STATES PATENTS 2,352,023 Schuller June 20, 1944 2,750,449 Thompson et al. June 12, 1956 2,773,120 Masterson Dec. 4, 1956 2,839,602 Fries June 17, 1958 2,866,012 Ginsburg et al Dec. 23, 1958 

11. A METHOD OF MAGNETIC RECORDING AND REPRODUCTING OF VIDEO SIGNALS WHICH COMPRISES THE STEPS OF RECORDING VIDEO SIGNALS ON A MAGNETIC TAPE IN SUCCESSIVE PARALLEL TRANSVERSELY EXTENDING LINES, THE END OF EACH LINE AND THE BEGINNING OF THE NEXT LINE BEING SIMULTANEOUSLY RECORDED WITH THE SAME SIGNAL AND AT SUBSTANTIALLY THE SAME RECORDING STRENGTH AS USED ALONG THE CENTRAL PORTION OF THAT LINE, AND REPRODUCING ONLY THE CENTRAL PORTION OF THE LENGTH OF THE RECORDED LINES INCLUDING PART OF THE RECORDED OVERLAP. 